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Marla Geha: Research

In the framework of modern cosmology, massive galaxies such as our Milky Way form hierarchically through the merging and accretion of small dwarf galaxies. Dwarf galaxies are defined as galaxies with roughly one tenth the mass of our Milky Way Galaxy or smaller. My research focuses on the properties of these dwarf galaxies and their differences from massive objects.

I maintain a research group wiki with a more updated list of research activities, including a list of possible research projects. If you are a prospective student and would like extra details on these projects, please email me to obtain access to the appropriate wiki pages.


Ultra-Faint Dwarf Galaxies
Collaborators: J. Simon

    In the past few years the number of satellite galaxies around the Milky Way has doubled. These newly discovered objects have luminosities similar to the faintest globular clusters, but kinematics and metallicities which firmly suggest that they are dwarf galaxies. We present Keck/DEIMOS spectroscopy for eight of these ultra-faint satellites. All are highly dark matter-dominated with mass-to-light ratios approaching 1000. These ultra-faint dwarf galaxies substantially alleviate the discrepancy between the observed number of Milky Way satellites and that predicted by standard Lambda Cold Dark Matter models.

  • Kinematics of the Ultra-Faint Milky Way Satellites
    Simon J., Geha M., 2007, ApJ, 670, 313

  • See the Keck Observatory press release or article in Discover magazine.

SDSS Low Mass Dwarf Galaxies
Collaborators: M. Blanton, A. West, M. Masjedi

NGC 205: An Tidally Interacting Dwarf Elliptical Galaxy
Collaborators: P. Guhathakurta, M. Rich, M. Cooper, K. Howley

    NGC 205 is the nearest example of a dwarf elliptical galaxy and the prototype of this galaxy class. A close satellite of the nearby large spiral galaxy Andromeda (M31), photometric evidence suggests that NGC 205 is gravitationally interacting with its parent galaxy. We have measured the internal dynamics of NGC 205 to significantly larger radius than previously possible by combining the velocity measurements of over 700 individual stars.

  • Internal Dynamics of Local Group Dwarf Elliptical Galaxies
    I. Mapping the Dynamics of NGC 205 Beyond the Tidal Radius

    Geha M., Guhathakurta P., Rich R. M., Cooper M. C. 2005, AJ, 131, 332

  • Unraveling the Interaction of NGC 205 with M31
    Howley K., Geha M., Guhathakurta P., Montgomery R., Laughlin G., 2006 in prep.

A Counter-Rotating Core in a Low Luminosity Elliptical Galaxy
Collaborators: P. Guhathakurta, R. van der Marel

    We present evidence for a counter-rotating core in the low-luminosity (M_B = -18.2) elliptical galaxy NGC 770 based on internal stellar kinematic data. This counter-rotating core is unusual as NGC 770 is not the primary galaxy in the region and it lies in an environment with evidence of on-going tidal interactions. We discuss several formation scenarios for this core and favor one in which NGC 770 accreted a small gas-rich dwarf galaxy during a very minor merging event. If this scenario is correct, it represents one of the few known examples of merging between two dwarf-sized galaxies.

  • NGC 770: A Counterrotating Core in a Low-Luminosity Elliptical Galaxy
    Geha M., Guhathakurta P., van der Marel R.P. 2005, AJ, 129, 2617

Optical Redesign of a Wide-Field Imaging Camera
    I was involved in a upgrade to an existing instrument at the Las Campanas Observatories in Chile. The Wide-Field CCD (WFCCD) is an imager and multi-object spectrometer in use at the du Pont 100-inch telescope. The previous CCD was a 2048x2048 chip which provides a 25 arcmin diameter field of view sampled at 0.77 arcsec/pixel which undersamples the point spread function and restricts the available field-of-view. Installation of a new 4064x4064 CCD is in progress. The new CCD will provide a slightly larger field-of-view with a smaller pixel size of 0.48 arcsec/pixel. This pixel size is much better matched to both the seeing typical at Las Campanas and the predicted optical performance of the instrument. The WFCCD field-of-view is comparable to that of IMACS on the Magellan telescope and will complement IMACS by providing pre-imaging capability for multislit spectroscopy work.

Dynamics of Dwarf Elliptical Galaxies
Thesis work at UCSC
Collaborators: P. Guhathakurta, R. van der Marel


Quasars behind the Magellanic Clouds
Collaborators: K. Cook, T. Axelrod, C. Alcock, A. Drake and the MACHO Collaboration

    The goal of this project is to identify a robust set of quasars behind the Magellanic Clouds for proper motion measurements. We have developed a technique to select quasar candidates from the stellar foreground using aperiodic variability in the MACHO database. Follow-up spectroscopy with the AAT+2dF and ANU's 2.3m telescopes have revealed over 50 previously unknown quasars at redshifts between 0.1 to 2.5. These quasars will serve as invaluable tools in studying the orbital motion of the Magellanic Clouds and consequently the size and shape of our Milky Way.

  • Variability-Selected Quasars in MACHO Project Magellanic Cloud Fields
    Geha, M. and the MACHO collaboration, AJ, 2003, 125, 1

  • The Proper Motion of the Large Magellanic Cloud using HST
    Kallivayalil N., van der Marel R.P., Alcock C., Axelrod T., Cook K.C., Drake A.J., Geha M. 2005, AJ, astro-ph/0508457

  • Download quasar data (last update Sept 2002)


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